1. Field of the Invention
The invention relates to water-based organopolysiloxane containing compositions, a process for their preparation and their use. The organopolysiloxane-containing compositions according to the invention are essentially free from solvents.
2. Discussion of the Background
Organosilanes of the general formula R.sup.0 -Si(OR.sup.1).sub.3, where R.sup.0 is an organic radical and R.sup.1 is a methyl or ethyl radical, have diverse uses, for example as adhesion promoters, release agents, rheology-improving agents, crosslinking agents and hydrophobicizing agents.
For ecological, work safety and economic reasons, changes are being made to using them in aqueous form. The following problems, in general arise here:
Alcohols are liberated by hydrolysis: EQU R.sup.0 -Si(OR.sup.1).sub.3 +3H.sub.2 O-R.sup.0 -Si(OH).sub.3 +3R.sup.1 OH PA0 The organosilane to be applied in water is not water-soluble: EQU R.sup.0 -Si(OR.sup.1).sub.3 +1.5H.sub.2 O-R.sup.0 -SiO.sub.1.5 +3R.sup.1 OH
Free alcohols lower the flash point of the solution for use, so that explosion-proof machines and special apparatuses must be employed for the essential processing steps. For toxicological reasons, the employees entrusted with handling the solution must be additionally trained and protected. Furthermore, disposal of the spent solution employed can present difficulties because of the hydrolysis alcohols. Special waste water clarification plants and also plants for after-treatment of waste gas or waste air are required.
The hydrolysate R.sup.0 -SiO.sub.1.5 formed according to this equation precipitates out of the reaction mixture as a polymeric silicone resin, so that it is no longer available for the desired use. Organosilanes having a very highly hydrophobic character, such as, for example, alkylalkoxysilanes, especially with a long or branched carbon skeleton, indeed hydrolyse only very slowly, but are not soluble in water.
To reduce the known disadvantages described above, the most diverse processes have been suggested in the past:
Some organosilanes, such as, for example, aminoalkyl-alkoxysilanes, are indeed water-soluble, but have only a limited usefulness in the various possible uses of organofunctional silanes. The introduction of further functional units, in particular on the basis of organosilanes which are water-insoluble per se, such as, for example, alkylalkoxysilanes, for example isobutyltrimethoxysilane, is desirable here. The measure of removal of hydrolysis alcohols by distillation during synthesis for preparation of organosilane formulations from only water-soluble organosilanes, such as, for example, from 3-aminopropyltriethoxysilane, is known. Water-based aminosilane systems which have a low alcohol content and are otherwise free from solvents are accessible in this manner and are available on the market, for example, in the form of DYNASYLAN.RTM. 1151.
The modification of water-based organosilane formulations of this type, with small amounts of organosilanes which are water-insoluble per se, such as, for example, methyltrimethoxysilane or vinyltrimethoxysilane, is described in unpublished European patent application entitled "Method for preparation of stable waterborne silane compositions". A molar ratio of the water-insoluble component to the water-soluble component of 1:2.5 can be achieved by this process. At a higher content of water-insoluble silanes, highly viscous products which gel in the course of time are formed. The use properties essentially correspond to those of the above-mentioned water-based organosilane formulations. Aqueous solutions which are stable for months and have relatively high contents of water-insoluble organosilanes, for example methyltrimethoxysilane or vinyltrimethoxysilane, are not accessible by this process. The preparation of aqueous solutions of highly hydrophobic silanes, such as, for example, isobutyltrimethoxysilane, is impossible in this manner.
In the emulsion method, which also belongs to the prior art, the organosilane which is water-incompatible per se is emulsified in water on liquid, water-insoluble silicone resin with the aid of emulsifiers (EP-A2 0 442 098, EP-B10 358 652 and U.S. Pat. No. 4,620,878). It is a disadvantage here that the products comprise considerable contents of surfactants as emulsifiers and can liberate considerable amounts of alcohol.
Formulation of silane combinations in water is disclosed in U.S. Pat. No. 5,073,195. The silane formulations are prepared from a water-insoluble alkyltrialkoxysilane and a water-soluble silane, such as, for example, an aminoalkylalkoxysilane, in a molar ratio of between 1:2 and 3:1. As can be seen from the examples of the U.S. patent specification, the formulations are prepared by hydrolysis of the silane mixture in less than the stoichiometric amount and by stripping of the reaction mixture at 60.degree. C. under reduced pressure, and for subsequent uses, the silane formulations thus obtained are also diluted with water. However, by dilution with water, the alkoxy groups which remain from the incomplete hydrolysis are split off in the form of the corresponding alcohol. The silane cohydrolysates disclosed in this reference comprise free alcohols in significant amounts and can furthermore liberate further amounts of alcohol by hydrolysis, which has an adverse influence on the use properties of the products.
The present invention is therefore based on the object of developing essentially solvent-free, water-based organosilane formulations which have the lowest possible content of free alcohols, have the highest possible flash point and liberate essentially no alcohols by hydrolysis on dilution with water.